Implement a basic version of /event_auth and /query_auth

[matrixbot]

This issue was originally created by @anoadragon453 at matrix-org/dendrite#758.

These endpoints aren't required in full for basic federation to work. We may just need to fill out the endpoints and have them return happy error codes without any content.

Individual tracking issues: matrix-org/dendrite#482, matrix-org/dendrite#757

[matrixbot]

This comment was originally posted by @clokep at matrix-org/dendrite#758 (comment).

Looks like event_auth was implemented and query_auth is no more so this can be closed I believe.